Identification guide · Minerals
How to Identify Augite
Augite forms short, stubby prismatic crystals with a nearly square cross-section, typically black, dark green, or brown, with a vitreous to dull luster and a colorless to pale gray-green streak. Hardness falls between 5.5 and 6, and its two cleavage directions meet at angles close to 87 and 93 degrees, a key diagnostic separating it from the amphibole group. It occurs embedded in dark volcanic groundmass far more often than as loose euhedral crystals, and beginners frequently mistake it for hornblende until the cleavage angle is checked.
Augite identification checklist
| Color | Black, Dark green, Brown | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous to resinous | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Translucent to opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 5.5–6 | It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. |
| Streak | Grayish green to colorless | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Good prismatic (~87°/93°) | |
| Fracture | Uneven | |
| Specific gravity | 3.2–3.6 | Heavier than it looks (specific gravity about 3.4000000000000004). |
| Crystal system | Monoclinic |
Augite look-alikes and how to tell them apart
Both sit near Mohs 5.5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Augite vs Aegirine →
Both sit near Mohs 5.5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Augite vs Diopside →
Both sit near Mohs 5.5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Augite vs Hornblende →
Andradite is harder (Mohs 6.5–7) than Augite (Mohs 5.5–6), so Andradite will scratch Augite and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
Augite identification FAQ
How can you tell if a rock is Augite?
Check the color (black, dark green, and brown), the vitreous to resinous luster, a Mohs hardness of 5.5–6 and a grayish green to colorless streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Augite?
Augite has a Mohs hardness of 5.5–6. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
What is the difference between Augite and Aegirine?
Augite (Mohs 5.5–6, vitreous to resinous luster) and Aegirine (Mohs 6–6.5, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Augite vs Aegirine comparison for a side-by-side table.
Is Augite worth anything?
Entry-level Augite specimens sell for around $2, typical collector pieces about $20, and premium examples $150 or more depending on size, quality and locality.
What color is Augite?
Augite is most often black, dark green, and brown. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
